2-(Thiocyanomethylthio)benzothiazole, TCMTB, is known to be useful in controlling bacteria and fungi in various aqueous systems. The preparation and use of 2-(Thiocyanomethylthio)-benzothiazole as a microbicide and a preservative is described in U.S. Pat. No. 3,520,976. U.S. Pat. Nos. 4,293,559, 4,866,081, 4,595,691, 4,944,892, 4,839,373, and 4,479,961 give examples of microbicidal properties of 2-(Thiocyanomethylthio)-benzothiazole. The disclosures of these patents are incorporated herein by reference.
2-(Thiocyanomethylthio)benzothiazole is known to be compatible with soluble oil, semi-synthetic and synthetic metalworking fluids. 2-(Thiocyanomethylthio)benzothiazole is manufactured by Buckman Laboratories International, Inc., and sold as Busan.RTM. 30WB, Busan.RTM. 1030, and Busan.RTM. 1118. These products are generally aqueous formulations of TCMTB. For example, Busan.RTM. 30WB product is a 30% by weight emulsifiable concentrate in water.
Although a good microbicide, 2-(Thiocyanomethylthio)-benzothiazole tends to be ineffective against bacteria under certain conditions, particularly at high pH. Some systems require high concentrations of TCMTB to effectively control the growth of microorganisms. These high concentrations are generally uneconomical.
Hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine has been used as a microbicide in the metalworking fluid industry for a long period of time. Hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine can be easily prepared starting from formaldehyde and ethanolamine. This compound is known in the trade as "triazine." Triazine is available from many companies as a solid or in varying concentrations in water under such commercial names as Grotan.RTM., Busan.RTM. 1060, etc. Triazine is available from Buckman Laboratories, Inc., as Busan.RTM. 1060.
As can be seen in Examples 1, 2 and 3, Table 1 (Samples 17-20), Table 2 (Samples 11-14), Table 3 (Samples 9-12), high concentrations of hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine are required to control both bacterial and fungal growth in metalworking fluids. One of the undesirable by-products of hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine, when used as a microbicide, is formaldehyde. Because of the carcinogenic properties of formaldehyde, it is desirable to use compounds that produce formaldehyde in the smallest quantities possible. However, when used in concentrations which produce only small amounts of formaldehyde, triazine is ineffective against fungi.
Both TCMTB and triazine have been used alone to control microorganisms in industrial fluids. Many industries, such as the machining industry, experience problems in industrial fluids caused by microorganisms. Aqueous metalworking fluids or cutting fluids used in the machining industry are particularly susceptible to fouling caused by microorganisms. In machining operations, metalworking fluids are used primarily to reduce friction and heat, thereby reducing wear and prolonging the life of equipment.
Metalworking fluids have properties which make the fluids ideal for the growth of bacteria and fungi. Although bacteria are important in the biodeterioration of metalworking fluids, fungi and yeast play a similar and important role as well. (Bennett, E. O., "The Deterioration of Metalworking Fluids," Proc. Industrial Microbiology, 13:121 (1974)).
Disadvantageously, these microorganisms can cause buildup of slime/microbial deposits on machine surfaces, the clogging of jets and lines, the deterioration of the properties of the metalworking fluid, enhanced corrosion, health and odor problems. The deterioration of metalworking fluids caused by the growth of microorganisms results in the loss of many of the fluid's essential properties. The pH of the fluid may drop and other chemical changes may occur until the fluid can no longer provide adequate lubrication. At this point, the fluid must be replaced with fresh fluid, which is costly and results in loss of production time.
The problems associated with the growth of microorganisms have resulted in the extensive use of microbicides in metalworking fluid systems. Microbicides may be incorporated in fluid concentrates or added directly to diluted fluids once they are in the holding tanks of the machine works. Of the commercially available microbicides, many have odor problems or create hazards with respect to storage, use or handling. Thus, the commercially available microbicides often possess limited utility. Consequently, workers in the trade have continued to seek improved microbicides.
Economic factors, particularly the cost of the microbicide and the expense of its application, are important when choosing a particular microbicide for use in metalworking fluid systems. The cost performance index of any microbicide is derived from the basic cost of the material, its effectiveness per unit weight, the duration of its biocidal or biostatic effect in the system treated, and the ease and frequency of its addition to the system treated.
Workers in the trade have sought commercially available microbicides capable of exhibiting a prolonged biocidal effect at economical use levels. Physical conditions, such as temperature and chemical reactivity with ingredients present in the system, often diminish or eliminate the effectiveness of known biocides. For example, many systems contain organic material which may react with a biocide and render it ineffective.